Heat exchanger and related exchange module

ABSTRACT

A heat exchanger, includes modules defining a first path for a first fluid, each having two metal sheets forming between them a network of channels which are located in parallel with each other from the fluidic point of view, each channel interposed between two neighbouring channels of the network being, over the whole of its developed length, adjacent to these two neighbouring channels from which it is isolated by two respective weld lines connecting the two metal sheets; a second path for a second fluid is defined between the modules; and an overall variation in the passage cross-section over the length of at least one of the paths with continuity of profiles of the channels.

This invention relates to a heat exchanger and a heat exchange moduleintended to form part of such an exchanger.

A heat exchanger is known from WO 98/16786 in which modules define afirst path for a first fluid, each one comprising two metal sheetsdefining between them a network of channels arranged mutually inparallel from the fluidic point of view. Each channel interposed betweentwo neighbouring channels of the network is, over the whole of itsdeveloped length, adjacent to these two neighbouring channels, fromwhich it is isolated by two respective weld lines joining the two metalsheets. A second path for a second fluid is defined between the modules,in the internal volume of a casing enclosing the modules.

According to this document, the modules are manufactured from two flatsheets, which are joined together by weld lines comprising theabove-mentioned lines isolating the neighbouring channels from eachother, then a pressurised liquid is introduced between the metal sheets,producing an inflation of the two metal sheets between the weld lines,thereby to form the channels. The channels of a same module are inparallel from a fluidic point of view between two distribution zonescommon to all the channels of a same module, themselves connected toconnecting boxes.

During the hydroforming step, i.e. the above-mentioned inflation step,the inflation in the distribution zones is limited so that when inoperation the second fluid more easily enters into pseudo-channelsformed between the neighbouring modules in the troughs between thesuccessive inflated zones. Apart from these zones of limited inflation,the profile of the channels is continuous and even uniform. Thus thefluid passage cross-sections are only modified locally at the inlet andoutlet. The transition between the modified passage cross-section zoneand the zone with a constant passage cross-section along the channels,is abrupt and localised.

WO 01/07 854 describes an improvement according to which the channelsare U-shaped instead of rectilinear. In a variant illustrated in FIG. 25of this document, a localised modification is shown of the passagecross-sections with an abrupt transition between the “normal” zone andthe modified zone acting as the inlet and outlet of the first and secondfluid in the first and second path, respectively.

DE-A1-19639115 describes a heat transfer element in the form of a plateconstituted by two metal sheets defining between them channels for anexchange fluid. In embodiments described with reference to FIGS. 4 and5, each channel has a general U-shaped configuration which is bifurcatedtwo times successively, such that the passage cross-section variesprogressively in a ratio of 1 to 4 from one end to the other of thebranched channel. Each channel thus folded back on itself and branched,occupies a rectangular space; the rectangular spaces being contiguous toeach other by their adjacent lengths. The purpose of this arrangement isto reduce the speed of the internal fluid when it has almost completedits exchange process, for improved calorific exchange in the zones wherethe two exchange fluids exhibit a small temperature difference betweenthem. The application indicated is a cooling element forhigh-temperature batteries for electric vehicles.

Such an exchanger is particularly complex to produce and its flow rateis very limited.

The object of this invention is to propose a heat exchanger whichwithout significant extra expense allows the progress of the flow ratesof at least one of the exchange fluids to be controlled, in particularwhen this fluid undergoes at least a partial change of state, forexample condensation, while flowing.

Another object of the invention is to produce a heat exchanger with lowpressure losses distributed in a controlled manner.

Another object of the invention is to propose a heat exchange modulewhich can be part of such an exchanger.

According to the invention, the heat exchanger in which modules define afirst path for a first fluid and each module comprises two metal sheetsforming between them a network of channels which are in parallel witheach other from the fluidic point of view, wherein each channel which isinterposed between two neighbouring channels of the network is, over thewhole of its developed length, adjacent to these two neighbouringchannels and is separated therefrom by two respective weld lines joiningthe two metal sheets, and a second path for a second fluid is definedbetween the modules, is characterised by an overall variation in passagecross-section along at least one of the paths, with the channels havingcontinuity of profile.

It has been found according to the invention that a structure of thetype described in WO 98/16 786 or WO 01/07 854, i.e. with channelsisolated from each other which are adjacent over their whole developedlength, is particularly suitable for implementation of overallvariations in passage cross-section along at least one of the paths.

By “overall” variation is understood a variation other than thelocalised path-end variations described above in relation to the priorart, and other than the local variations due for example to the factthat the second exchange fluid, if circulating transversally to thechannels, experiences for example a reduction in passage cross-sectioneach time it passes an inflated part of one of the two adjacent modules.

By “continuity of profile of the channels” is indicated that thevariations in passage cross-section are not due to profilediscontinuities such as cross-sectional variations due to abruptwidening or narrowing, variations due to bifurcation of a single channelinto two channels.

The overall variations in cross-section may be obtained according to theinvention by channels of different hydraulic diameters, by channels thehydraulic diameter of which varies progressively from one end to theother, and/or by a relative arrangement of the modules which varies thehydraulic diameter between the modules for the second fluid and/or etc.

The hydraulic diameter of a passage for a fluid is the diameter of atheoretical cylindrical tube offering the same flow resistance as thepassage in question having a profile other than a circular cylinder.

According to a second aspect of the invention, the heat exchange modulecomprising two metal sheets forming between them a network of channelswith continuous profile arranged in parallel to each other from afluidic point of view, each channel interposed between two neighbouringchannels of the network being adjacent over the whole of its developedlength to these two neighbouring channels from which it is isolatedrespectively by two weld lines joining the two metal sheets; ischaracterised by an overall variation in the passage section defined bythese channels with continuity of profile of the channels.

Other features and advantages of the invention will become apparent inthe following description, which relates to non-limitative examples.

In the attached drawings:

FIG. 1 is a perspective view, with a cut-out, of a vertical-flowparallel current plate heat exchanger;

FIG. 2 is a perspective view of a cross-current plate heat exchanger,the flow in the modules—or plates—being vertical;

FIG. 3 is a perspective view of a plate condenser with the platesarranged in vertical planes and rising gas flow.

FIG. 4 diagrammatically illustrates, two modules according to a firstembodiment of the invention, in a perspective view.

FIGS. 5 to 8 are views similar to a portion of FIG. 4 but illustratingfour other embodiments of the invention;

FIG. 9 is a diagrammatic sectional view of a heat exchanger moduleaccording to yet another embodiment, during the course of itsmanufacture by hydroforming in a die;

FIG. 10 is a view of a variant in order to produce a half-die;

FIG. 11 is a perspective view of a heat exchange module according to yetanother embodiment;

FIGS. 12 and 13 are elevational views of two embodiments for a bundle ofmodules according to FIG. 11;

FIG. 14 diagrammatically illustrates a perspective view of a bundleobtained with modules according to a modification of FIG. 11; and

FIG. 15 is a view of another embodiment of a bundle of modules for aheat exchanger according to the invention.

Generally, in the interests of clarity, all the drawings of thisapplication are very diagrammatic, the number of channels in a modulebeing markedly lower than would be found in most real situations, andthe metal sheet thickness is represented as unduly large.

FIGS. 1 to 3 very diagrammatically show different types of heatexchangers by way of illustration, to enable a better understanding ofthe invention.

In the example shown in FIG. 1, the heat exchanger comprises a casing 1with a rectangular profile with respect to the vertical axis, containinga stack of heat exchange modules 2 in the general form of plates,extending along vertical planes. Each module 2 is essentially made up oftwo metal sheets 3, which are welded together along vertical weld lines4, and which are inflated between these weld lines 4 to define betweenthem the vertical channels 6.

Each channel extends with a continuous profile over the whole height ofthe module 2. All the channels 6 open at each upper and respective lowerend, into an upper connection chamber 7 defined in an upper connectingbox 8 or respectively in a lower connection chamber 9 defined in a lowerconnecting box 11. Thus the channels 6 together constitute a firstexchange path for a first fluid and this first exchange path may, inoperation, be connected by the connecting boxes 8 and 11 to an externalcircuit for this first fluid. The sealed connection of the channels 6 tothe chambers 7 and 9 is provided by bars 12 of a suitable shape whichare inserted between the ends of the modules 2 and together form a basefor the connecting box 8 or 11 respectively. The channels 6 are thus inparallel from a fluidic point of view with each other between the twoconnection chambers 7 and 9. Each channel 6 apart from the two endchannels of the network of channels of each module is adjacent over itswhole developed length to two neighbouring channels, while beingisolated from these two neighbouring channels by a respective weld line4 which is continuous over the whole developed length of the channel. Inthe case illustrated here where the channels are rectilinear, thedeveloped length is the same as the overall length. In other cases wherethe channels are curved and for example have a U-shape as in WO 0107854,the developed length is of course very different to the bulk length.

A second path for a second exchange fluid is defined between the modules2. The inlet and the outlet in this second path are by means of secondconnecting boxes 13 and 14 located on the side wall of the casing 1 toenable their internal chambers 16 and 17 respectively to communicatewith the gaps 18 between the edges of modules 2, on the side of the ends19 of the bars 12 which faces away from the connection chamber 7 or 9.In the example of the connecting box 13, its periphery is leak-tightlywelded to periphery 22 of a rectangular opening formed in casing 1. Oneside 21 of the periphery 22 is formed by the aligned ends 19.

Thus a second exchange fluid flows between the connecting boxes 13 and14, passing through a second exchange path constituted by the internalspace of casing 1 located between modules 2.

In the example shown, the lateral connecting box 13 is located in theupper part close to the upper connecting box 8 for the first path, whilethe lateral connecting box 14 is located on the lower part of casing 1close to the lower connecting box 11 of the first path. The second fluidenters laterally between the modules, flows between the modules parallelto the channels 6, then exits laterally by the other connecting box.Each of these two fluids may flow upwards or downwards according to theapplication. The name “counter-current exchanger” describes an exchangerwith parallel currents in which the two fluids flow in oppositedirections, one upwards and the other downwards in this example. Thename “co-current exchanger” describes an exchanger in which the twofluids flow not only parallel, but also in the same direction.

The example shown in FIG. 2 will only be described in so far as itdiffers from that shown in FIG. 1.

In this example, the lateral connecting boxes for the second path 13 and14 completely cover two opposite sides of the casing 1; these sides thenbeing entirely open such that the second fluid flows in a horizontaldirection parallel to the planes of modules 2. Such an exchanger wherethe two fluids flow in different directions is known as a“cross-current” exchanger.

The example in FIG. 3 will only be described in so far as it differsfrom that shown in FIG. 2. In this cross-current exchanger, the channels6 are oriented horizontally; the modules 2 still being in verticalplanes. The path of the first fluid is therefore directed horizontally.In contrast, the connecting boxes for the second fluid 13 and 14 areplaced under and over the case 1 such that the direction of flow of thesecond fluid is vertical between the modules 2. In the example moreparticularly shown in FIG. 3, this concerns a condenser. The lowerconnecting box 13 comprises an inlet 23 for a gas and the upperconnecting box 4 comprises an outlet 24 for the residual gas part fromthe inlet flow 23. When this flow 23 passes between the modules 2, thechannels 6 of which have cooling fluid such as, for example, cold water,passing through them, the condensable part of the second fluid formsdroplets which fall back into a bottom 26 of the connecting box 13 andare then evacuated through a lower outlet for liquid 27.

In such a condenser, the second fluid has a volume flow rate whichdecreases from the inlet 23 to the outlet 24, as the initial volume ofgas decreases to the extent that a part of the gas condenses.

Consequently, if the passage cross-section of the second path isapproximately the same for the whole length of this second path betweenthe inlet connecting box 13 and the outlet connecting box 14, the speedof flow will decrease. If this is an appropriate speed at the inlet ofthe second path, it will be too slow for effective exchange near theoutlet. If, on the other hand, the speed is appropriate in the region ofthe outlet, it will be too high at the inlet and the gas will have atendency to carry droplets along with it towards the outlet, contrary tothe separation effect sought.

This example of a condenser has been chosen to clearly demonstrate theadvantages of a different passage cross-section in different zones ofthe same path, but other examples can be envisaged, in particular in anevaporator, or also to adapt the speeds in the meaning of anoptimisation of the result obtained, in particular in terms of heatexchanges.

In the example shown in FIG. 4, each module 102 comprises channels 6_(a), 6 _(b), 6 _(c), 6 _(d), having different hydraulic diameters.

In the example of FIG. 4, the pitch of the weld lines 4, i.e. thedistance between the successive weld lines 4 is equal to a constantcalled P_(o). The difference in hydraulic diameter between neighbouringchannels is obtained by a difference in inflation of the metal sheets 3in each zone defining a channel; channels 6 _(a) to 6 _(d) havinginflation amplitudes G_(a) to G_(d) respectively, which increase fromone edge to the other of the module 102. The profile and consequentlythe hydraulic diameter of each channel 6 _(a), 6 _(b), 6 _(c), or 6 _(d)are constant over the whole length of this channel.

When two modules 102 as described are placed side-by-side in parallelplanes P, with the modules of the same hydraulic diameter placed facingeach other, the available hydraulic diameter in the second path 28between these modules 102 in a direction perpendicular to that ofchannels 6 _(a) to 6 _(d) varies overall from one end to the other ofthe second path. If for example the second path is ascending, in theconfiguration shown where the channels have a hydraulic diameterincreasing from bottom to top, the hydraulic diameter of the second pathdecreases from its beginning to its end. This corresponds to the desiredcharacteristics in the condenser in FIG. 3 according to the explanationsgiven above.

In the example shown in FIG. 5, which will only be described withrespect to its differences in relation to the example in FIG. 4, eachmodule 202 comprises groups of channels having identical hydraulicdiameters; however these diameters being different from one group toanother. In the diagrammatic representation of FIG. 5, there are twogroups each of two channels, namely the lower group of channels 6 _(a),6 _(b) with an identical relatively small hydraulic diameter, and theupper group of channels 6 _(c) and 6 _(d) with an identical relativelylarge hydraulic diameter. Here once again, the differences in diameterare the result of different levels of inflation with an identical pitchP_(o). Consequently, the second path 28 comprises a first hydraulicdiameter between the channels 6 _(a) and 6 _(b) of the neighbouringmodules 202, and a second smaller hydraulic diameter between theneighbouring channels 6 _(c) and 6 _(d).

In the example in FIG. 6, which will only be described with respect toits differences in relation to the example in FIG. 5, between the twogroups of channels 6 _(a), 6 _(b) and 6 _(c), 6 _(d) there is anintermediate channel 6 _(e) with an inflation of 6 _(e) which has anintermediate value between the lower value of channels 6 _(a) and 6 _(b)and the higher value of channels 6 _(c) and 6 _(d). Consequently, thehydraulic diameter 6 _(e) is intermediate between that of channels 6_(a) and 6 _(b), and the larger value of channels 6 _(c) and 6 _(d).Furthermore, the second path 28 has between the channels 6 _(e) of theneighbouring modules 302, an intermediate value between the larger onedefined between the channels 6 _(a) and 6 _(b) and the smaller onedefined between the channels 6 _(c) and 6 _(d).

In all the examples described up to this point the pitch P_(o) betweenthe weld lines 4 was the same for all the weld lines for one module andfor all of the modules. In the example shown in FIG. 7, the inflationsG_(o) are the same for all the channels of all the modules 402. Incontrast, the channels of a network comprise a first group of channels 6_(g) and a second group of channels 6 _(h). The pitch P_(g) between twoweld lines defining between them a channel 6 _(g) is greater than thepitch P_(h) between two weld lines defining between them a channel 6_(h). In this example, the hydraulic diameter of the path 28 decreaseswhen the pitch of the weld lines decreases.

The example shown in FIG. 8 combines the pitch and inflation variations.There are four channels 6 _(j), 6 _(k), 6 _(m), 6 _(n) with pitchesP_(j) to P_(n) which increase regularly and inflations G_(j) to G_(n)which also increase regularly from bottom to top of each module 502.

FIG. 9 illustrates the hydroforming stage to produce a module with fourgroups of channels 6 _(p), 6 _(q) 6 _(r) 6 _(s), having differenthydraulic diameters resulting at least in part from different levels ofinflation. Before injection of the hydroforming liquid, the flat blankof the module, comprising at this stage two flat metal sheets weldedtogether, for example by laser welding, along the weld lines such as 4in the previous figures, between dies 31, 32 which between them define acavity with working surfaces 33 _(p), 33 _(q), 33 _(r), 33 _(s), and 34_(p), 34 _(q), 34 _(r), 34 _(s) respectively, between which the moduleblank is laid and which have between each pair of surfaces, a distancecorresponding to the required inflation in each area respectively. FIG.9 shows the result obtained after differentiated inflation of thedifferent channels following separation of the working surfaces betweenwhich they are located.

FIG. 10 illustrates less expensive tooling in which each die (only thelower die 31 is shown) has a flat working surface 33 corresponding tothe maximum inflation envisaged, and separate shims 36 _(p), 36 _(q), 36_(s) to define the zones where less inflation is required.

For the upper die 32 (not shown in FIG. 10), the shims should be fixedbelow the working surface of the die to avoid them moving by gravitybefore the hydroforming stage. For the lower die, it is also desirablefor the shims to be fixed.

FIGS. 9 and 10 also illustrate that the invention enables the hydraulicdiameters to be varied in a first direction, for example in thedirection of increase, for example between the groups 6 _(p) and 6 _(q)or 6 _(q) and 6 _(r), then in a second direction, here the direction ofdecrease between the group 6 _(r) and 6 _(s), when this is required tooptimise the exchanger.

In all the examples described with reference to FIGS. 4 to 8, the weldlines 4 of a module are mutually parallel and the hydraulic diameter ofa channel is constant over its whole length.

In the example represented in FIG. 11, the weld lines 604 of a module602 are all convergent; in this example towards a single point situatedbeyond one of the ends of the module. In other words, the neighbouringweld lines between them form a relatively narrow angle, labelled as A inFIG. 11. Thus, the pitch between successive weld lines increases fromone end to the other of each channel, as does the hydraulic diameter ofthe channel. Such a module has an isosceles trapezoidal general shape,with oblique longitudinal sides 37 which are approximately parallel tothe two outside weld lines 604 of the network of channels.

Such a module is useful in order to produce a condenser in aconfiguration according to FIG. 1 or FIG. 2; i.e. with verticalchannels. If the large end of the channels is facing upwards, the fluidto be condensed may follow a descending path within the channels whereit encounters a hydraulic diameter which decreases in relation to thereduction in volume of the fluid by condensation. The second fluid, forexample water, passes between the modules, or may form a bath betweenthe modules. With the same arrangement of modules, an ascending-flowevaporator can also be produced; the first fluid encountering increasinghydraulic diameters as its volume increases due to evaporation.

Such a module can also be arranged with the large end of the channelsdownwards in order to produce, for example, a reflux condenser; i.e. asdescribed above with reference to FIG. 3, with an increasing evaporationflow and droplets forming which flow back to the base and into acollector.

The inflation of the channels may be constant along each channel, oralternatively may increase from the narrower end to the wider end ofeach channel.

FIG. 12 shows an elevation view of a bundle of modules 602 with channelswhere the inflation increases from bottom to top and where the modulesare in parallel vertical planes. In the example shown in FIG. 13,modules 602 identical to those in FIG. 12 are placed in planes whichconverge towards a point located above the narrow end of the channels soas to reduce the hydraulic diameter of the second path on the side wherethe ends of the channels are narrow, in relation to the embodiment inFIG. 12.

FIG. 14 shows the bundle very diagrammatically when the inflation isconstant along each channel of the modules according to FIG. 11. Thebundle has the shape of a hexahedron in which the two opposite faces areisosceles trapeziums in parallel planes. A casing for such a bundletypically has a corresponding shape, with two opposing parallel faces inthe shape of an isosceles trapezium and two rectangular faces joiningthe oblique sides of the trapeziums.

If, moreover, the inflations of the channels are variable as illustratedin FIGS. 12 and 13, the bundle takes the general shape of a truncatedpyramid, i.e. the two trapezoidal faces are inclined in relation to eachother and the two other lateral faces also become trapezoidal. Thecasing typically has a corresponding shape.

In the example shown in FIG. 15, the modules 702 have channels which areall identical with the same widths and the same inflations over thewhole of their length. These modules are arranged in a fan-shape inrelation to each other, thus in oblique planes with respect to eachother, converging beyond one end of the channels such that the hydraulicdiameter of the second path, assumed to be for co-current orcounter-current, varies from one end to the other.

In a way which is not shown, it is also possible to position the modulesin relation to each other in a fan shape by relative pivoting about anaxis parallel to the weld lines, thus to the longitudinal direction ofthe channels, in order to produce a variable hydraulic diameter of thesecond path when the exchanger is the cross-current type.

In the examples in FIGS. 1 to 3, the modules 2 are offset in relation toeach other in their own plane such that the peaks of undulation of onemodule are located opposite the troughs of undulation of the twoneighbouring modules. This arrangement favours circulation in the secondpath following a transverse direction to the channels, whether for across-current exchanger (FIGS. 2 and 3) or for the entry of the secondfluid by a side opening and the exit of the second fluid by another sideopening in the case of a parallel-current exchanger (FIG. 1). However,in order to simplify the illustrations, all the examples given withreference to FIGS. 4 to 8, 14 and 15 represent another possiblearrangement, with the undulations of two neighbouring modules facingeach other peak-to-peak and trough-to-trough. This is simply by way ofillustration, and the invention is equally applicable with an offsetarrangement, for example the one in FIGS. 1 to 3.

The invention is particularly applicable with the following dimensions:

-   developed length of channels: 0.5 to 10 m-   width of the network of channels: 0.15 to 2 m-   pitch sequence of modules: 8 to 105 mm-   pitch sequence of weld lines: 10 to 100 mm-   inflation of channels: 5 to 80 mm measured inside the channels.

The metal sheets are typically of stainless steel of a thickness of afew tenths of a millimetre (no upper limit at 10/10) with theunderstanding that a thin sheet is preferable for thermal exchange butthat the pressure differences between the two fluids and the thermalstresses must also be taken into account.

Of course, the invention is not limited to the examples described andrepresented. The means of varying the hydraulic diameter described maybe combined in very many ways.

It is conceivable to produce channels which have a constant hydraulicdiameter over one part of their length and a progressively variablehydraulic diameter over another part of their length.

The exchangers described with reference to FIGS. 1 to 3 are not in anyway limitative. For example, if the exchange modules are arrangedwithout offsetting between them, thus with the undulations facingpeak-to-peak, it is possible to locally reduce the inflation of thechannels in the zones envisaged for the lateral introduction of thesecond fluid, in a similar manner to that described with reference toFIG. 25 of WO 01/07 854. When the second fluid is a bath, the casing maybe unnecessary.

The invention is compatible with non-rectilinear channels, for examplethe U-shaped channels of WO 01/07 854.

With respect to the example in FIGS. 11 to 14, it is also possible tohave modules in which:

-   -   the inflation varies progressively along each channel;    -   the pitch between weld lines, on the other hand, is constant.

1. A heat exchanger comprising: modules defining a first path for afirst fluid, each comprising two metal sheets forming between them anetwork of channels which are located in parallel with each other fromthe fluidic point of view, each channel interposed between twoneighbouring channels of the network being, over the whole of itsdeveloped length, adjacent to these two neighbouring channels from whichit is isolated by two respective weld lines connecting the two metalsheets; a second path for a second fluid is defined between the modules;and an overall variation in a passage cross-section over the length ofat least one of the paths with continuity of profiles of the channels.2. A heat exchanger according to claim 1, characterised in that thepitch between the neighbouring weld lines varies progressively over atleast part of the length of the channels of one module.
 3. A heatexchanger according to claim 1, characterised in that the inflation ofthe metal sheets of a module varies progressively over at least part ofthe length of the channels.
 4. A heat exchanger according to claim 1,characterised in that the pitch between neighbouring weld lines variesfrom one channel to the other of a module.
 5. A heat exchanger accordingto claim 1, characterised in that the inflation of the metal sheets of amodule varies from one channel to another.
 6. A heat exchanger accordingto claim 1, characterised in that the arrangement of the modules inrelation to each other produces an overall variation in the passagecross-section over the length of the second path.
 7. A heat exchangeraccording to claim 1, characterised in that the overall variation in thecross-section of one of the paths is in the same direction as avariation in the flow rate of gas in this path intended for a phasechange process.
 8. A heat exchanger according to claim 1, characterisedin that the modules are in parallel planes.
 9. A heat exchangeraccording to claim 1, characterised in that the modules are inconvergent planes.
 10. A heat exchanger according to claim 1,characterised in that the modules have longitudinal edges forming anangle with each other, each being almost parallel to a respectiveoutside weld line.
 11. A heat exchange module comprising two metalsheets which between them form a network of channels located in parallelto each other from a fluidic point of view, each channel interposedbetween two neighbouring channels of the network being adjacent over itswhole developed length to these two neighbouring channels from which itis isolated by two respective weld lines joining the two metal sheets,and wherein an overall variation in the passage cross-section is definedby the channels with continuity of profile of the channels.
 12. A heatexchange module according to claim 11, characterised in that the pitchbetween neighbouring weld lines varies progressively over at least partof the length of the channels.
 13. A heat exchange module according toclaim 11, characterised in that the inflation of the metal sheets variesprogressively over at least part of the length of the channels.
 14. Aheat exchange module according to claim 11, characterised in that thepitch between the neighbouring weld lines varies from one channel theother.
 15. A heat exchange module according to claim 11, characterisedin that the inflation of the metal sheets varies from one channel to theother.
 16. A heat exchange module according to claim 11, characterisedin that it comprises longitudinal edges each forming an angle with theother, each being almost parallel to a respective outside line of weld.